Electric furnace



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ELECTRIC FURNACE Filed May 20, 1944 6 Sheets-Sheet 5 June 7, 1949. F. F. POLAND ELECTRIC FURNACE Patented June 7, 1949 ELECTRIC FURNACE Frank F. Poland, Rome, N. Y., assignor to Revere Copper and Brass Incorporated, Rome, N. Y., a

corporation of Maryland UNITED STATES PATENT OFFICE Application May 20, 1944, Serial No. 536,580

11 Claims. (CI. 13-20) My invention relates to electric furnaces.

The invention, which has among its objects the provision of an electric furnace which will be air tight and free from the deleterious eflects of expansion of the furnace structure, will be best understood from the following description and accompanying drawings of an embodiment of the invention, the scope of which latter will be more particularly pointed out in the appended claims.

In the drawings- Fig. 1 is a section on the line i-l of Fig. 2, with parts in elevation;

Figs. 2 and 3 are, respectively, sections on the lines 2-2 and 3-3 of Fig. 1, with parts in elevation;

Fig. 4 is a rear elevation of the furnace according to Figs. 1, 2 and 3;

Fig. 5 is an isometric view, with parts broken away, of the body portion or lining of the furnace chamber;

Fig. 6 is a section on the line 6-6 of Fig. 1 on an enlarged scale, with parts omitted;

Fig. 7 is a fragmentary elevation on an enlarged scale of parts shown by Fig. 4;

Fig. 8 is a section on the line 8-8 of Fig. '7; and

Fig. 9 shows a detail.

Although many features of a furnace according to the invention are of general application, the furnace shown by the drawings, although not limited to such use, is particularly applicable for use in the practice of the methods disclosed by applicant's co-pending application Serial Number 519,887, filed January 27, 1944, now Patent 2,429,584, issued October 21, 1947. In such a furnace a molten copper base alloy containing zinc is treated under non-oxidizing conditions by heating it to a high temperature in the presence of carbonaceous material for removing its zinc content, the carbonaceous material conveniently constituting the lining or body portion of the furnace chamber containing the molten metal.

When such a furnace is of large size it has been found most suitable to build up this lining of carbon blocks, and, for insuring against entrance of air through the interstices of the furnace walls, to surround those walls with an imperforate metal casing which operatively tightlyfits those walls and for economic reasons is preferably of mild steel, it being understood that entrance of air into the furnace chamber would not only make it difllcult to treat the molten metal under non-oxidizing conditions but also would tend to destroy the carbonaceous lining by what amounts to combustion of the same. With a fur-- nace so constructed extreme difficulty has been encountered in preventing the metal casing from overheating and from being ruptured by stresses imparted by expansion of the furnace walls when the latter are heated, it being understood that the interior of the furnace when used for practicing said method commonly will be atabout 3200 F. and that the mild steel metal casing if heated in excess of about 350 F. will soften and lose its structural strength.

Referring to the drawings, the furnace illustrated comprises a lower portion l and aremovable cover portion 3 (Figs. 2 and 4). The lower portion comprises a metal casing, preferably of mild steel, having the four lateral walls 5 and a bottom wall 1, the joints between these walls being welded together to form an integral air tight structure. As shown, the bottom of the casing is supported on the spaced I-beam supports 9 extending transversely of the casing. Also, as shown, the casing is reinforced by the vertical corner angle-irons II (Figs. 1 and 4) welded to the walls 5, between which angle-irons extend, at the front and rear of the furnace, the horizontal I.-beams i3 welded thereto, spacing strips H- being placed between the I-beams and casing and welded to each so that the I-beams as well as the angle-irons II are in substance integral with the casing. The end walls of the casing, as shown, are reinforcedby the vertically extending I-beams l5 welded to those walls so as in substance to be integral therewith.

The cover of the furnace similarly comprises a metal casing, preferably of mild steel, having the top wall I! and four lateral walls l9 (Figs. 2 and 3). The vertical corners between the lateral walls l9 are welded to each other and to the'vertical bars 20, one of which latter is placed at each corner of the cover and extends from above the top wall l1 downward to intermediate the height of the lateral walls. The upper edge of each of the walls l9 and the corresponding edges of the top wall I! throughout their by the angle-irons 25 extending about the interior of this portion of the casing at the lower edges of the lateral walls I9, to which walls the angle-irons pthe lateral walls I of the lower portion of the casing and interiorly of those walls are angleirons 21 extending entirely about the casing and welded thereto, the horizontal legs of the angleirons 25 resting upon the horizontal legs of the angle-irons 21 when the cover of the furnace is placed on the lower portion of the furnace.

For making an air tight joint between th lateral walls 6 of the casing for the lower portion of the furnace and the lateral walls It of the easing for the cover portion of the furnace, the last mentioned walls have welded thereto horizontal I- beams- 29 which extend for the full length of each side of the cover, the lower ends of the bars 20 abutting with'the top edges of these I-beams at the corners of the cover and being welded thereto. Carried by these I-beams is a member extending entirely about the cover comprising the horizontal top plate 3| and spaced downwardly projecting vertical plates 38, the innermost of the wholly constituted by the block ii.

are horizontal plates 3'! coextensive therewith,

which plates 31 carry the spaced upwardly projecting plates 39 coextensive with said plates 31.

' When the cover is in position the plates 33 enter tom block 4i, the block 43 also extending entirely I across the furnace. As shown, the block 43 is provided above its lower surface with an opening 45 (Figs. 2 and 5) through which extends a conduit 41 for supplying molten metal to the furnace chamber. As shown, this conduit has a downwardly projecting spout 49 which extends into a hollow II of a cup-shaped block 53, the metal entering the furnace through the conduit zinc condenser.

this block having an opening 62 through which the conduit it passes. To insure against leakage of metal about the exterior of the conduit it is necessary for it tightly to fit the opening in the furnace walls through which it passes, which assurance cannot be had if the block 6! should rest on the extreme top of the adjacent block 4| as does the block 43 at the opposite end of the furnace. Consequently the adjacent block M is downwardly recessed as shown at 83, while the block II is extended downward to fill said recess, thus enabling the walls of the opening 62 to be Th upper portion ofthe transverse wall comprising the block 6| may .be built up to thelevel of the top of the transverse block 43 by a block 65 of \the same length as the block 6|, the two preferably having a tongue and groove fit 'as indicated at 6 (Figs. 2 and 5). Normally the conduit II is closed by a removable screw-threaded graphite plug 69 which may be turned by a key wrench inserted through the exterior open end of the conduit, and to insure against leakage the portion of the conduit at the, right of the plug, as viewed in Fig. 2, may be normally filled with fireclay and closed by a removable cap ll.

Zinc fumes and the like may be discharged from the furnace chamber through a suitable conduit 12, which in practice, when the furnace is used for treating zinciferous metal, leads to a closed As shown, the opposite longitudinal walls of the body portion or lining of the furnace chamber are constituted by blocks 13 of non-graphitic carbon extending-for the full length of the chamber, the transverse blocks at the ends of the chamber being recessed as indicated at I! (Figs. 1 and 5) for receiving the end portions of the blocks 13.

Preferably the carbon blocks constituting the body portion or lining of the furnace chamber are accurately machined to fit with each other,

41 overflowing the rim of the block into the furnace chamber to fill the latter with molten metal to the level L (Figs. 2 and 3), while the. hollow ii of the block is kept filled with molten metal to seal the spout of the conduit so as to prevent entrance of air into the furnace chamber and to prevent escape of zinc or other fumes therefrom. As shown, the upper surface of'the bottom of the lining is recessed at Iii and the adjacent portion of the inner surface of the block I3 recessed at 51 (Fig. 5-) to receive the block I to hold it in position. Conveniently the conduit 41 and block I are formed of graphite to facilitate machining of the same.

Molten metal may be discharged from the furnace chamber through a conduit 59, preferably formed of graphite, the bore of which conduit communicates with said chamber at the level of the upper surface of the blocks 4|, as illustrated in Fig. 2, so that all the molten metal in the chamber may be drained therefrom when desired. The adjacent end wall portion of the furnace chamber with which the molten metal contacts is constituted by a block 8 I, of non-graphitic carbon,

adjacent surfaces being formed with keyways 11 which receive elongated nongraphitic carbon keys It to lock the parts together. These keyways alsov act to prevent escape of molten metal from the furnace chamber should the same tend to leak through the joints between the blocks. For further insuring against such leakage the lateral wallsof the chamber are surrounded by an integral layer 8| of. carbonaceous material. This material may be applied in the form of a thick paste rammed into the space between the carbon blocks and the surrounding brickwork, a space several inches in width being left between the carbon blocks and the surrounding brickwork to permit entrance of the paste. This paste may be the material known as green electrode paste consisting of a mixture of comminuted carbon and coal tar, and being the material commonly employed for making molded carbon electrodes. After the furnace is in operation the paste will bake and form an integral layer of hard carbon. As shown, the exterior sides of the blocks 43 and I at the two extreme transverse sides of the carbon lining project slightly beyond the adjacent sides of the end blocks 4| forming the bottom of which extends for the full width of the chamber, the bottom of the lining. Under the high temperature conditions at which the furnace is operated graphite has remarkably high lubricating or anti-friction properties, and permits the heavy furnace lining to expand freely on the brickwork which supports the lining on the bottom of the metal casing.

As illustrated in Fig. i, surrounding the carbon layer 8| is a layer formed of the bricks 81 and slabs 89, while surrounding the slabs 89 is a layer of bricks 9I, the space between the latter and the lateral walls 5 of the casing being filled by a layer of lagging 98. The bricks 81 and slabs 89 are preferably formed of highly refractory fireclay of high alumina content, preferably of the quality known as "60% alumina. This material will withstand and operate efficiently at temperatures up to about 3000 F. Consequently the lateral walls of the furnace lining should be of such thickness as to reduce the temperature at the exterior of the carbon layer II to at least such value. For furnaces in which the hottest portions thereof, namely, the portions below the resistors hereinafter referred to, are at about 3200 F. this will mean a thickness of the blocks constituting the carbon lining of about 18 inches, and a thickness of about 12 inches above those portions where the furnace is not quite as hot. It however will be understood that where lower temperatures are employed the lining need not be as thick, while 'if firebricks which are less heat refractory are employed the lining must be thicker for a given furnace temperature than would otherwise be necessary. The carbon lining, although extremely heat; refractory, is a relatively poor heat insulator, while the material described for the layers 81 and 89, although not as heat refractory, is a better heat insulating-material. Hence, by employing the layers 81 and 89, not only may the carbon walls be made thinner, but the overall thickness of those walls and the layers 81 and 89 may be made thinner than if that overall thickness were constituted by walls of carbon.

The bricks of the layer 9| which surrounds the layers 81 and 89 are preferably common insulat ing firebricks which, although having better heat insulating properties than the material of the layers 81 and 89, are less heat refractory. Consequently the total thickness of the layers 81 and 89 should be such as to reduce the temperature applied to the layer 9I to that which the bricks constituting the latter will withstand and at which they will operate most efliciently as a heat insulating layer, say a temperature not exceeding 2300 F. Where, for example, the internal tem-- perature of the furnace is about 3200 F. and the carbon lining is of the specific thickness above mentioned, satisfactory results will be secured when the total thickness of the layers 81 and 89 is about 6% inches.

The heat refractory lagging 98 employed is resiliently yieldable, so as to permit the interior furnace structure to expand and contract horizontally on the anti-friction layer 85 without injury to the metal casing of the furnace. This laging material is preferably prefabricated slabs of porous fibrous silicious dianiataceous material such as the material sold under the name Insulag. It resembles ordinary sheet magnesia lagging, which latter material in fact can be substituted for it where much lower temperature conditions are employed. The material will withstand and operate efllciently at temperatures not exceeding about 1800 F., and the thickness of the layer 9| is therefore such as to reduce the temperature applied to the lagging to one not cause overheating of the metal and at the same time will permit the internal furnace structure to expand without injury to the casing. Ordinarily under the temperature conditions mentioned the lagging may be about 1 inch thick, and such thickness will take care of the expansion of furnaces up to about 15 feet long or wide.

The brickwork below the of the furnace lining may consist of an outer layer '85 of firebrick of the same material as the bricks of the layer 9i about the lateral walls of the lining, and, between the layer 89 and the carbon slabs or plates 85, a further layer 81 of flrebrick of the same material as the layers 81 and 89.

As shown, the carbon blocks 08, 8| and I8 forming .the lateral walls of the furnace chamher are formed to provide a shelf 88 adjacent their tops, upon which shelf rest plates 88, preferably of graphite,.extending entirely across the furnace chamber. Upon these plates rests a body IOI of refractory insulating material, preferably broken charcoal. When electric current is passed through the resistors hereinafter described the same are heated to incandescence. The plates 99 above the resistors become incandescent as well as the interior walls of the carbon blocks, the plates 88 and the resistors acting to reflect heat downward on the surface of the metal being treated.

As shown, the cover of the furnace comprises a flat arch comprising the superimposed wedgeshaped blocks I03 (Fig. 3) extending lengthwise of the cover at opposite sides thereof, and the wedge-shaped blocks I05 (Fig; 2) extending transversely of the cover at opposite ends thereof, these blocks resting upon the horizontal webs of the angle-irons 25 and abutting with the lateral walls I9 of the metallic casing of the cover. Extending transversely across the furnace and supported by the wedge-shaped blocks are blocks I0'I of non-graphitic carbon. Resting upon these blocks is a layer I 09 of refractory heat insulating firebrick, and between the latter and the top wall of the casing for the cover is a layer III, preferably of insulating silicious cementitious material. As shown, the blocks I 01 are formed with a recess II8 of V-shaped cross-section as viewed in Fig. 3. In building the furnace the relatively finely broken up mass III' of charcoal is distributed on the plates 99 in amount just about sufllcient to fill the recess II3, care being taken not to have an excess amount so that when the cover is put in position it, owing to its great weight which in a furnace of the size hereinafter mentioned will be in the order of .14 tons, will not exert such pressure on the plates 99 as will break them. The lug bars 20 hereinbefore referred to are preferably provided with perforations II 4 for adapting the cover to be attached to a crane hoist so that it may be removed and replaced. r

The longitudinally extending carbon blocks 13 of the furnace lining, as shown, are further formed to provide shelves 1. These shelves serve to support the bar-like resistors II9,'which latter are preferably formed of graphite. For a furnace chamber, which at its bottom is about 9 feet, long I .connection to suitable hoses.

7 these resistors may be about inches in diameter spaced about 16 or 1'! inches apart.

As shown, the ends of the resistors are connected for series flow of current by plates III. preferably of-graphite, these plates being supported on the shelves III by blocks I22 of heat refractory electric insulating material such as sintered aluminum oxide AlsOs of high purity, say about 99.5%, the ends of the resistors being screwthreaded, as shown in Fig. l, and secured to the plates by graphite clamping nuts I23. As shown in Figs. 1 and 6, the openings I25 in the plates I'll through which the resistors extend are elongated lengthwise of the plates so that the resistors, although securely clamped thereto by the nuts III, may slide longitudinally of the plates to permit expansion and contraction of the series of resistors longitudinally of the furnace particularly when the walls of the latter expand and contract, it being understood that graphite has high lubricating or anti=friction qualities when heated to incandescence. As shown, the ends of the resistors are secured by means of graphite coupling sleeves I11 to large diameter graphite extensions I29 projecting'through openings IlI in the adjacent carbon block 13 in spaced relation to the wallsof such opening. In alignment with the openings ISI the furnace walls and easing are formed with openings through which the enlarged sleeves are of heat refractory electric insulating material preferably alundum. As shown, the space between-the walls of each sleeve and associated extension is packed with a yieldable layer I of asbestos or other yieldable heat refractory material, so that the extension despite the packing remains operatively in spaced relation to the surrounding walls of the sleeve in the sense that relative movement between them transversely of the extension is not prevented.

As best illustrated in Fig. 8, screw-threaded on the enlarged diameter end portion Ill of each resistor extension I29 is the base I91 of a terminal I39, preferably. formed of copper, the base being insulated from the walls of the metallic furnace casing by a washer I of yieldable refractory insulating material such as asbestos. As shown, the base III :is provided with the radial water pasages It! with which communicate the water supply passage Ill and water discharge passage I leading to the end of the terminal for The water circulated through the base and terminals keeps them and the adjacent portions of the resistor extensions I29 cool. Because of the cooling water and the increased diameter of the resistor extensions ascompared to the diameters of the heating resistors, although the latter are heated to incanably of asbestos, being placed between the ring and the plate for rendering the joint between them air tight. As its opposite end the sleeve,

descence the terminals and adjacent portions of the extensions, including the portions of the latter within the sleeves III, are kept relatively cool. As shown, each terminal I59 extends through an opening I45 in a plate Ill of insulating materminals, as otherwise the bar In is liable to as showrnis welded at I5I to a metal ring I59 which is secured tothe metal furnace casing, preferably by welding as shown at, I85.

The sleeves I41 in conjunction with the packings I95 insure against entrance of air into the furnace chamber through the openings in the furnace wall through which the resistor extensions I29 pass. At the same time the sleeves being laterally yieldable prevent undue stresses being imparted to the resistor extensions when the metal casing of the furnace expands, and likewise permits the resistor extensions to move relative to the casing in so far as they tend to so move by reason of relative expansion between the metal casing and the walls of the furnace interiorly of the casing.

For supporting the terminals I39 and the resistor extensions against the stresses of the cables connected to the terminals, in the embodiment of the invention shown the two insulating plates I are connected to the opposite ends, respectively, of a bar I61, which latter is rigidly supported by posts I59 (Fig. 4) carried by a plate "I (Fig. 3) secured to the projection ends of the I- beam supports 9 for the furnace As shown, metal plates I13 are welded at I-15 to the ends of the bar I61, while the insulating plates I45 are secured to these metal plates by bolts I11, the perforations I19 in the plates I13 through which the bolts pass being elongated in the direction of the fixed bar [51 so as to permit relative movement longitudinally of the furnace between the plates I45 and that bar.

The current employed for energizing the resistors commonly will be in the order of 6,000 to 10,000 amperes, and when this is an alternating current a very strong alternating electro-mag-' netic field is set up about the terminals and resistor extensions I29. It has been found that this field is sufilcient seriously to overheat the portions of the casing walls adjacent the resistor extensions when the casing is of steel because of the hysteresis phenomena involved. To avoid this effect, in the present embodiment of the invention the portion of the lateral walls 5 of the casing adjacent each resistor extension is constituted by an insert I9I of non-magnetic material, preferably silicon bronze which has a tensile strength in the order of steel. As shown. each insert is of the same thickness as the rest of the lateral walls ofthe casing and is secured thereto by a metal frame I53 welded to the insert and the lateral walls 5. As shown, the inserts extend farther from the terminals toward the center of the length of the furnace than toward the ends of the furnace because the electro-magnetic field is strongest between the two terminals. When an alternating current is employed, also the bar I51 preferably is provided with an insert I of non-magnetic material, such as copper or silicon bronze, for breaking the magnetic path between the regions adjacent the loverheat and weaken.

9 Likewise the metal of the sleeve I41 and the rings ill and I associated with said sleeve are preferably of non-magnetic material, such as bronze, ,to prevent their overheating when analternating current is employed.

invention as the material most suitable for resisting high temperatures and abrasion, blocks of other forms of heat refractory elemental carbon, such as graphite. may be employed. Also it will be understood that, although blocks of material presenting exposed inner surfaces of elemental carbon at the surface level of the pool of metal in the furnace chamber must be employed when the furnace is used for practising the method of applicant's copending application hereinbefore mentioned considering all aspects of said method, blocks which are composed of carbon or graphite or which otherwise present elemental carbon surfaces necessarily need not in all instances be employed when the furnace is used for other purposes, it being obvious that there may be employed blocks of any refractory suitable for the use to which the furnace is put and the temperature at which it is operated. Further it will be understood that, although-the furnace illustrated and described herein has a furnace chamber of elongated rectangular horizontal cross-section, it obviously may, if desired, be square in horizontal cross-section, and that the word rectangular" in this connection is used in the appended claims where the context admits.

in its generic sense as including both rectangles and squares.

It will be understood that within the scope of the appended claims wide deviations may be made from the form of the invention described without departing from the spirit of the invention.

I claim:

1. An electric furnace having, in combination, walls forming a furnace chamber; said walls comprising a furnace lining, a refractory support for said lining, and refractory anti-friction means between said lining and support for facilitating expansive movement of said lining relative to said support; a metallic casing for said walls, and a layer of yieldable lagging between the lateral portionsofsaid walls and the lateral walls of said casing for permitting over all expansion of the former independently of the latter.

2. An electric furnace having, in combination,

walls forming a furnace chamber, a metallic g0 casing for said walls; said walls comprising a furnace lining forming the interior bottom and side surfaces of said chamber, refractory heat insulating material between said lining and the bottom and side walls of said casing, a layer of refractory anti-friction material between the bot- ,1 tom portion of said lining and adjacent surface of said insulating material, and a layer of yieldable lagging between the side walls of said casing and adjacent surfaces of said insulating material for permitting over all expansion of the furnace ,walls independently of said casing.

3. An electric furnace, having, in combination walls forming a furnace chamber, a metallic casangels I 10 lining forming the interior bottom and side-surfaces Of said chamber, refractory heat insulating material between said lining and the bottom and side walls of said casing, an anti-friction layer of graphite between the bottom portion of said lining and adjacent surface of said insulating material, and a layer of yieldable lagging between the side walls of said casing and adjacent surfaces of said insulating material for permitting over all expansion of the furnace walls independently of said casing.

4"." electric furnace having, in combination. walls forming a furnace chamber, a metallic casing for said walls; said walls comprising a furnace lining of non-graphitic carbon forming the interior bottom and side surfaces of said chamber, a fire brick layer between said lining and the bottomand side walls of said casing. an antifriction layer of solid graphite between the bottom portions of said lining and the fire bricklayer beneath it for supporting said lining on such layer, and a layer of yieldablelagging between the side walls of said casing and the flre brick layer at the corresponding sides of said lining for permitting over all expansion of the furnace walls independently of said casing.

5. An electric furnace having, in combination, a pot-like furnace chamber of elongated substantially rectangular horizontal cross-section, the bottom wall of which pot-like chamber is formed of a course of elongated non-graphitic carbon blocks each extending from one longitudinal side of such pot to the other, the end side walls of said pot-like chamber being formed of elongated blocks of like material resting on said bottom course and extending from one side of such pot to the other, the longitudinal side walls of said pot-like chamber being formed of elongated blocks of like material resting on said bottom course with the opposite ends of each of said blocks abutting with the opposed sides of the blocks forming the end side walls of such pot, a block of one of said side walls extending be- -low the upper level of said bottom wall, which latter is recessed to receive such block, and a discharge conduit for the chamber extending through the last mentioned block from adjacent said upper level of said bottom wall to the outer side of said block.

6. An electric furnace having, in combination, a pot-like furnace chamber of elongated substantially rectangular horizontal cross-section, the bottom wall of which pot-like chamber is formed of a course of elongated non-graphitic carbon blocks each extending from one longitudinal side of such pot to the other. the transverse end walls of said pot-like chamber beingformed of elongated blocks of like material resting on said bottom course and extending from one side of such pot to the other, the longitudinal side walls of said pot-like chamber being formed of elongated blocks of like material resting on said bottom course with the opposite ends of each of said blocks abutting with the opposed sides of the blocks forming the transverse end walls of such pot, a fire brick layer having a portionbeneath such pot for supporting it and a portion sur-' brick layer and a bottom on which said layer is supported, and a layer of resilient lagging between said layer and the side walls of said casing.

7. An electric furnace having, in combination,

ing for said walls; said walls comprisingafurnace 76 a pot-like furnace chamber of elongated substantially rectangular, horizontal cross-section,

the bottom wall of which pot-like chamber is sides of the blocks forming the transverse end.

walls of such pot, a fire brick layer having a portion beneath such pot for supporting it and a portion surrounding the lateralwalls of such pot,

a metallic casing having side walls surrounding said fire brick' layer and a bottom on which said layer is supported, an anti-friction layer of graphite between the bottom of such pot and said layer, and a layer of resilient lagging between said layerand the side walls of said casg. 8. An electric furnace having, in combination,

'a pot-like furnace chamber of elongated substantially rectangular horizontal cross-section, the bottom wall of which pot-like chamber is formed of a course of elongated non-graphitic carbon-blocks each extending from one longitudinal side of such pot to the other, the transverse end walls of said pot-like chamber being formed traction of said casing independently. of said walls of said casing and fire brick layer.

10. An electric furnace having, in combination, a pot-like furnace chamber of substantially rectangular horizontal cross-section, the bottom wall of which pot-like chamber is formed of a course of elongated blocks each extending from one side of such pot to the other, the side walls of said pot like chamber being formed of elongated blocks resting on said bottom course and extending for at least the full length of the corresponding interior side of the pot-like chamber with the end portions of the blocks at each side of said chamber in abutting relation with the end portions of the blocks at the two opposite sides of said chamber transverse thereto, a fire brick layer having a portion beneath such pot of supporting it and a portion surrounding the lateral walls of such pot, a metallic casing having 7 side walls surrounding said fire brick layer and a bottom on which said layer is supported, a layer of anti-friction material between the bottom of such pot and said fire brick layer, and a layer of resilient lagging between said fire brick layer and the side walls of said casing.

11. An electric furnace having, in combination, heat refractory walls forming a furnace chamber, a heat conductive exteriorly exposed metallic casing for said walls in laterally spaced relation thereto, a resiliently yieldable packing layer in the space between said walls and casing for permitting overall expansion of said walls indeof elongated blocks of like material resting on said bottom course and extending from one side of such pot to the other, and the longitudinal side walls of said pot-like chamber being formed such pot; the opposed vertical faces of the blocks of said bottom course. and the upper horizontal faces thereof and opposed faces of said blocks resting thereon, having longitudinally extending complementary horizontal key-ways, and the and faces of the blocks forming the longitudinal sides of "such pot and, opposed faces of the blocks forming the transverse ends of such pot having vertically extending key-ways, and keys in such key-ways.

9. An electric furnace having, in combination, a pot-like furnace chamber of substantially rectangular horizontal cross-section, the bottom wall of which pot-like chamber is formed of a course of contacting elongated blocks each extending from one side of such pot to the other, the side walls of said pot-like chamber being formed of elongated blocks resting on said bottom course adjacent its edges and extending for at least 7 the full length of't'h'e corresponding interior side pendently of the casing and contraction'of the casing independently of said walls, said walls comprising a furnace chamber lining of heat refractory carbonaceous material, electric heating means within said chamber for heating said lining to high incadescence, said walls also comprising a heat insulating layer between said lining and packing layer contacting with both, which heat insulating layer is less heat refractory than said lining but more heat refractory than said packing layer, the thicknesses of said lining and heat insulating layer relative to their heat conductivities being such as caused to be applied to said heat insulating layer and packing ting relatlonwith the end portions of the blocks at the two opposite sides of said chamber transverse thereto, a fire brick layer having a portion beneath such pot for supporting it and a portion surrounding the lateral walls of such pot, a substantially air tight metallic casing having sidev walls surrounding said fire brick layer and a bottom on which said layer is supported, and a resiliently yieldable packing layer of heat insulating material between said fire brick layer and the side walls of said casing for permitting overall REFERENCES CITED The following referecnlces are of record in the file of this-patent:

UNITED STATES PATENTS Number Name Date Re. 18,420 Shaw Apr. 12, 1932 1,533,224 Colby Apr. 14, 1925 1,641,764 Keenan Sept. 6, 1927 1,674,947 Bunce June 24, 1928 1,742,286 Shaw Jan. 7, 1930 1,825,011 Navvatiel Sept. 29, 1931 1,857,103 South May 3, 1932 2,061,250 Perkins Nov. 17, 1936 2,134,785 Goldberg Nov. 1, 1938 2,351,490 Cooper June 13, 1944 FOREIGN PATENTS Number Country Date 952 Great Britain 1880 OTHER REFERENCES "Industrial Furnaces, vol. 1, by W. Trinks (3rd edition), pages 263 and 324.

Certificate of Correction Patent No. 2,472,612. June 7, 1949.

- FRANK F. POLAND It is hereby certified that errors appear in the printed specification of the above ,numbered patent requiring correction as follows:

Column 11, line 49, claim 8, for the word such read said; column 12, line 18, claim 10, for of supporting read for supporting; line 45, same claim, for as caused read as to cause;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 15th day of November, A. D. 1949.

THOMAS F. MURPHY,

Am'etant Oammim'oner of Patents.

' Certificate of Correction Patent No. 2,472,612 June 7, 1949 FRANK F. POLAND It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 11, line 49, claim 8, for the word such read said; column 12, line 18, claim 10, for of supporting read for supporting line 45, claim 11, for as caused read as to cause; a

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oifice.

This certificate supersedes Certificate of Correction issued November 15, 1949. Signed and sealed this 13th day of December, A. D. 1949.

THOMAS F. MURPHY,

Am'etant Oommz'sszoner of Patents. 

